Safety pilot assembly for burners



R; L.BERGMANN 2,882,735

SAFETY PILOT ASSEMBLYVFOR BURNERS Filed April 27, 1951 April 21 1959 [wr I i l 5 Fl 1 4 I i x I 55 54 5 52 Z v u =nnnnnnnnnr" I l me tutor: R.L. B21; EMANN. 04 21 4 #1 (Ittorneg United States Patent "ice SAFETYPILOT ASSEMBLY FOR BURNERS Richard L. Bergmann, Columbus, Ohio, assignorto Surface Combustion Corporation, Toledo, Ohio, :1 corporation of OhioApplication April 27, 1951, Serial No. 223,338

3 Claims. (CI. 74-58) The present invention relates to safety pilots forgas burners and more particularly to a safety pilot which shall be welladapted for use with gas-conversion burners for house heating furnaces.In safety pilots of this type it is desirable that the cycling time, orelapsed time after the pilot flame goes out until the safety functionoperates, be independent of ambient furnace temperatures, that thecycling time be easily adjustable after the safety pilot is installed ina furnace, and that the apparatus be sturdy and reliable in service. Thepresent invention provides a safety pilot which embodies these features.

For a consideration of what I believe to be novel and my inventionattention is directed to the following specification and the concludingclaims thereof.

In the drawing:

Fig. 1 shows the improved safety pilot applied to a gas conversionburner for a house heating furnace, only a part of the furnace beingshown.

Fig. 2 is a side elevation, with parts in section, of apparatusembodying the present invention Fig. 3 is a partial sectional view of aportion of the assembly shown in Fig. 2.

Fig. 4 shows a modification of a detail shown in Fig. 3.

Fig. 5 shows a simplified schematic diagram of an elec trical controlsystem for use with the improved safety pilot.

Fig. 6 is an enlarged view of a portion of the apparatus of Fig. 2.

A gas conversion burner unit for an ordinary househeating furnace 11 isgenerally indicated at and comprises a casing 12 which extends throughthe rash-pit doorway of the furnace. The unit also comprises a removablecover 12' over a parts-supporting platform in front of the casing 12. Amixing tube 13 extends through the casing 12 into the furnace chamberfor delivering fuel to a burner head 14 positioned in said chamber. Asafety pilot 15 is mounted next adjacent the burner head 14 to insuresafe operation of the burner. The burner head 14 is shown as of thesingle-port flame-retention type. Mounted above the burner is adeflector 16 to accelerate combustion and to deflect the burning gasestowards the side walls of the furnace chamber, The mixing tube 13receives gas from means comprising a supply pipe 17 hav ing a controlvalve 20 (see Fig. 5).

The support for the safety pilot 15 comprises a horizontally disposedframe 21 and an upright bracket 22 mounted on said frame. The safetypilot comprises a thermostat generally indicated at 23, the thermostatcomprising an inclined expansion rod 24 having a lateral extension 27,and an upright rod 25, the two rods being welded at their lower ends toa base 26 and welded to each other at their upper ends whereby theassembly forms a triangular structure of three rigid members 24, and 26.An upright heat-shield extends loosely between the two legs or rods 24and 25 so that heat from a small flame 28 from a pilot burner 33 mayselectively heat the expansion rod 24, and by differential expansionPatented Apr. 21, 1959-.

of that rod over the rod 25 causes the top or lapex 23 of the triangularstructure to move with respect to the base 26, it being understood thatthe upright rod 25 is flexed about its lower end by said expansion.

The base 26 constitutes the top of a pedestal 29 which is secured bybolts 31 to 'a shelf 32 forming part of the frame 21. The pilot burner33 is supported on a shelf 18 on said pedestal 29. A gas-controllingorifice-fitting 34 is threaded into the bottom of the pilot burner 33. Agas-supply tube 35 delivers gas to the orifice fitting 34, and the jetof gas issuing from that orifice draws air Into primary air holes 36 inthe side wall of the pilot burner 33. The gas-air mixture so formedissues from ports 37, 38 and 39 adjacent the top of the pilot burner,the top being closed. Where a variety of fuel gases are to beaccommodated by the pilot burner, the quantity of air entrained by saidjet of gas may be varied by varying the size of the primary air holes36.

The extension 27 of the expansion nod 24 pushes against the upper end ofa lever 40 which is fulcrumed intermediate its end on the uprightbracket 22 by a relatively thin and short metal strip 41 havingsufficient shear strength to bend like a hinge without offsetting, thusgiving rise to no lost motion. A flexing length of 0.0625 inch for asteel strip of 0.025 inch thickness has been found to be suitable,giving a ratio of length to thickness in the hinge strip of five to twoor 2 /2/ 1. Softer materials may require a lesser ratio to operatewithout oft"- setting. The hinge strip 41 is secured to the bracket 22and to the lever 40 by clamping plates 42 and 43 secured thereto as byrivets 44. To the lower end of the lever 40 there is connected one endof a push rod 46, the rod being threaded into the lever 40 to permit theeffective length of the rod to be varied for a reason presentlyappearing. The rod 46 extends through a square hole in an upturned end53 of a bracket 52 secured as by screws 54 to a side wall 48 of theframe 21, the rod being slidable in said hole but being square so it maynot tum therein. The rod also extends part-way through an axial bore inan elongate switch operating member 50, hereinafter sometimes called acam member, the rod being slidable in said bore but the bore and rodbeing square so that the member may not turn on said rod. A cylindricaladjusting rod 47 having a knurled knob at one end is turnable in a holein an upturned end 45 of the bracket 52. The rod is internally bored andthreaded to screw on to the adjacent threaded end 49 of the push nod 46and is externally threaded to extend into 'a threaded bore in theadjacent end of the elongate member 50. The leads of the internal andexternal threads on the rod 47 vary a sufficient degree to give amicrometer-type adjustment between the member 50 and the rod 46. Singlelead threads of thirty-two and thirty-six threads per inch are suitablefor this purpose. In order to prevent the rod 47 from being unscrewedfrom the rod 46 and from the member 50, the rod may be provided with afixed collar 56 and the member 50 may be provided with an arm 57 fixedlysecured to the latterand having a downturned extension 51 disposedbehind the collar to form a stop therefor. Instead of a collar 56 onsaid rod 47, the body of the latter may have a neck portion as shown inFig. 4 to provide a shoulder 58 adapted to abut the stop 51 to limitrearward movement of rod 47. A spring 60 between the member 50 and theupturned end 53 of the bracket 52 tends to take up any slack in theconnections between the rod 46 and the extension 27 of the thermalelement 23.

Mounted on the top side 59 of the frame 21 is a switch mechanism 55having a spring blade actuating arm 55'. The elongate member 50 isprovided with a neck portion 19 wherein the free end of theswitch-actuating arm 55' tends to project, the neck portion beingprovided to form a shoulder 20 which, upon the member 50 being movedtowards the right as shown in Fig. 2, will cause the free end of thesaid arm 55' of the switch 55 to ride up on the shoulder 20 and thusactuate the switch 55.

A spark electrode 77 is secured next adjacent the pilot burner port 37for initial ignition of the pilot gas. vThe gas from the pilot burnerports 38 and 39 is ignited from port 37 by a runner flame issuing fromthe small slots connecting the ports 37, 38 and 39. The gas from theport 38 is adapted to ignite the main burner 14, and

the gas from port 39 is adapted to warm the expansion rod 24 of thethermal element 23.

In Fig. a transformer 61 provides 24 volts A.C. to

operate an electrical control system for the burner and the coil 64 to aroom thermostat 66 which is in turn con- 1 nected by lead 67 to thetransformer 61. A cold contact 70 of the switch 55 is connected by alead 71 to a spark transformer 72 and thence by lead 73 to a vibratingreed 74 of which only the contact is shown, and which is in turnconnected by leads 75 and 67 to the transformer 61. The sparktransformer 72 is connected on the high voltage side to ground by lead76 and to a spark electrode 77 which is adapted to discharge a spark tothe pilot riser 33 next adjacent the pilot burner port 37.

In operation, when power is supplied to the 24 v. transformer 61, andthe pilot burner is out, the switch 55 is on its cold contact 70, andthe contact of the reed 74 is closed. A spark is released at the pilotburner port 37 to ignite gas issuing therefrom. Flame from the pilotburner port 39 warms the expansion leg 24 of the thermal element 23which thereupon moves towards the left to push on the lever 40. Thelever 40 pivots about the hinge 41 and moves the adjusting rod 46axially to move the switch arm 55 to its hot position, breaking thecircuit to the spark electrode and placing the power circuit to the maingas valve under control of the room thermostat 66 as is conventional. Inthe event that the pilot flame goes out, the thermal element 23 moves tocold position, and the spring 60 forces the adjusting rod assembly andthe of expansion such that at a furnace temperature, say, of 400 F., thenecessary movement of the apex 23' is but .030 inch, and since the rate:of cooling of the rod 24 is slower in the hot furnace,- this maycompensate for the shorter movement required to still give a cycle timeof 60 seconds from time of pilot failure to time of opening of thecontacts of the switch mechanism 55. It is apparent that, in thisexample, the apex 23' of the thermal element has moved .010 inch towardsclosing the contacts of switch 55 upon raising the furnace chambertemperature from 100 F. to 400 F. with the pilot burner oif. In this wayconstant cycling time, or elapsed time between failure of the pilot andopening of the safety switch 55, is maintained over a wide range offurnace chamber ambient temperatures. The relatively small movement ofthe apex 23' of the thermal element is accurately adjusted in a floatingmicrometer assembly by turning a single handle, and unintentional overadjustment is made virtually impossible.

Having disclosed my invention, I claim:

1. An adjusting rod assembly comprising an elongate rod having first andsecond threaded portions at its respective ends, rod means havinginternal and external threads having the same direction of advance butdifferent leads, the internal thread being adapted to receive the secondthread of said rod, a cam member having an internally threaded portionadapted to receive the external thread of said rod means, and said rodand said cam member being non-turnable with respect to each other i andthe rod extending into a bore in said cam member whereby turning saidrod means axially moves the cam member and said rod with respect to theother.

2. An adjusting rod assembly according to claim 1 I comprisingstop-means for limiting relative axial motion of said cam member andsaid rod means whereby to prosaid rod may be slidably supported and asecond hole lever 40 to follow, thus moving the switch arm 55' to its Anace chamber temperatures the switch is operated at the same relativepoint. For example, if in a relatively cold furnace at 100 F. havingonly the pilot burner operating, and the flame 28 playing on theinclined expansion rod 24, upon failure of the pilot burner the apex 23'must move .040 inch to open the contacts of the switch mechanism 7 55,and does so in seconds cooling time, then in a relatively hot furnacethe same cooling time is desirable for opening those contacts. This canbe obtained by using materials in rods 24 and 25 having dissimilarcoeflicients axially aligned with said first hole wherethrough said rodmeans may be slidably supported, said first hole being non-circular andadapted to support a non-circular portion of said rod whereby to preventrotation thereof with respect to said bracket, and elastic means actingaxially between said cam member and said bracket in a manner tendingalways to move said cam member axially with respect to said bracket.

References Cited in the file of this patent UNITED STATES PATENTS1,819,697 Boudette Aug. 18, 1931 2,012,503 Gauger Aug. 27, 19352,017,725 Newell Oct. 15, 1935 2,192,629 Beam Mar. 5, 1940 2,192,632Beam Mar. 5, 1940 2,266,721 Christiansen Dec. 16, 1941 2,291,805 DenisonAug. 4, 1942 2,305,243 English Dec. 15, 1942 2,578,608 Shull Dec. 11,1951 2,589,804 Harris et al Mar. 18, 1952 2,649,152 Mayer et al. Aug.18, 1953

